Functions.h

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/* Copyright 2016 Kristofer Björnson
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef COM_DAFER45_TBTK_FUNCTIONS
#define COM_DAFER45_TBTK_FUNCTIONS

#include "TBTK/UnitHandler.h"
#include "TBTK/Streams.h"
#include "TBTK/TBTKMacros.h"

#include <cmath>

namespace TBTK{

class Functions{
public:
    static double fermiDiracDistribution(
        double energy,
        double mu,
        double temperature
    );

    static double boseEinsteinDistribution(
        double energy,
        double mu,
        double temperature
    );
private:
};

inline double Functions::fermiDiracDistribution(
    double energy,
    double mu,
    double temperature
){
    double e = UnitHandler::convertNaturalToBase<Quantity::Energy>(
        energy - mu
    );
    double t = UnitHandler::convertNaturalToBase<Quantity::Temperature>(
        temperature
    );
    if(t != 0.){
        return 1./(
            exp(
                e/(UnitHandler::getConstantInBaseUnits("k_B")*t)
            ) + 1.
        );
    }
    else{
        if(e < 0.)
            return 1.;
        else if(e == 0.)
            return 0.5;
        else
            return 0.;
    }
}

inline double Functions::boseEinsteinDistribution(
    double energy,
    double mu,
    double temperature
){
    double e = UnitHandler::convertNaturalToBase<Quantity::Energy>(
        energy - mu
    );
    double t = UnitHandler::convertNaturalToBase<Quantity::Temperature>(
        temperature
    );

    if(t != 0.){
        return 1./(
            exp(
                e/(UnitHandler::getConstantInBaseUnits("k_B")*t)
            ) - 1.
        );
    }
    else{
        TBTKExit(
            "Functions::boseEinsteinDistribution()",
            "Bose-Einstein distribution not well behaved at T=0.",
            "Use Model::setTemperature() to set a non-zero temperature."
        );
    }
}

};  //End of namespace TBTK

#endif